Encyclopedia of Environmental Science and Engineering, Volume I and II

540 INSTRUMENTATION: WATER AND WASTEWATER ANALYSIS

and its use. There must be no perturbation of the sample

composition or physical characteristics which will nullify

or seriously distort the analysis results and be detrimental

to the purposes of the analysis.

Preservation is a means of preventing decomposition

and change of various biological or chemical components in

the sample. Standard Methods provides a treatment for the

preservation of specific components in a variety of samples

where preservation is possible (see Table 1).^2

Sampling Considerations Two types of changes must be

considered in order to define and carry out a proper sam-

pling program, i.e., time-based changes in the source to be

sampled and in the sample taken from the source.

Time-based changes in the source may be short or long

term. The short-term changes taking place are indicative of

biological, chemical, and/or physical interactions in the time

span assigned to repetitive sampling. Long-term changes

in the sources are related to ecological trends. It is impor-

tant to be aware of each of these types of changes so that

sample storage changes are not mistaken for sample source

changes.

In order to obtain a legitimate sample of water or waste-

water for analysis one must understand the nature the sample

and its time-based changes. Once a sample taken from the

source it may begin to change for many reasons as discussed

in the previous section, IIA, 1. The sample must be represen-

tative of the sample source, that is it must have the same bio-

logical, chemical, and physical characteristics of the source

at the time the sample is taken. Therefore the sampling pro-

cedure must not cause a change in the sample relative to the

source if there is to be an accurate correspondence between

the sample analysis and the nature of the sample source at

the time the sample was taken.

To prevent confusing the two variables, ecological changes

in the source and interactions in the sample that can occur in

the same time span in a series of samples, preservation of

the samples is undertaken to deter changes after sampling.

However, preliminary sampling and testing may be necessary

to indicate the type of time-based changes occurring. Then a

reliable program can be established with some certainty.

Three kinds of sampling schemes are undertaken in

consideration of the sample source characteristics—grab,

composite and integrated samples.

A grab sample is one taken at a given time and place.

If the source doesn’t change greatly during a long passage

of time or within a large distance in all directions from

the sampling point, the grab sample is useful. The results

from grab samples are said to represent the source for the

given values of distance from sampling location and time.

However a time and place series of grab samples is needed

to establish the constancy of analytical values for different

times and distances from the original grab sampling point.

With that information the sampling frequencies and times

for a sampling program can be established. The sampling of

solids, such as, benthic muds and sludges, requires great care

in order to obtain truly representative samples.

A series of samples collected and blended to give a

time-averaged sample is known as a composite or time-

composite sample. In another procedure the volume of

each sample of the series collected is proportional to flow

of the sample source, namely the water body or waste

stream. The samples of various volumes are composited

to provide the final time-composite sample. This type of

sample gives an average value over a time period and saves

analysis time and cost. Sampling frequencies and the total

time span of the series depends on the source. Composite

sampling may be used for process streams to determine

the effect of unit processes or to monitor a plant outfall

for daily or shift changes. However, biological, chemical,

and physical parameters that changes on storage during

the sampling time period can’t be reliably determined in

time-composited samples and another sampling protocol is

needed (see Table 1).

At times, simultaneous samples are needed from various

locations within a given source, such as a river or lake. Grab

samples are then composited, usually based on volumes pro-

portional to flow, and are called integrated samples. These

samples are used to determine average composition or total

loading of the source which varies in composition in its

breadth and depth. The sampling program for such sources is

complex and requires careful consideration for each unique

source.

Water and Wastewater Parameters

A large number of water quality parameters are utilized in

the characterization, management and processing of water

and wastewater. Table 2 lists a number of these param-

eters separated into three categories—physical, chemical

and biological. It is obvious that only some parameters are

considered to be pollution factors because they indicate con-

ditions of water during processing or in the natural state.

The STORET system of the USEPA lists more than four

hundred parameters separated into six major groups and is

used for the analysis, collection, processing and reporting of

data.^3 Table 3 gives a sampling of groups of parameters in

this system. Not all of these parameters are used frequently,

since many are rather unique to particular waste effluents. In

actuality, a very small number are used in the analysis of a

particular sample.

Water quality parameters may be divided into two groups,

specific and non-specific water quality parameters. Specific

parameters refer to chemical entities of all types, e.g., ions,

elements, compounds, complexes, etc. For example, in

Table 2 some specific parameters are ammonia, all metals

listed, dissolved oxygen, nitrates, sulfates, and so forth. Non-

specific parameters are included in three categories and some

examples are as follows: chemical (hardness, alkalinity, acid-

ity, BOD [biochemical oxygen demand], TOC [total organic

carbon], COD [chemical oxygen demand], chlorine demand),

physical (salinity, density, electrical conductance, filterable

residue), and physiological (taste, odor, color, turbidity, sus-

pended matter). Many of these non-specific parameters are

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